The present invention relates generally to automatic turning machines and, more particularly, to multiple spindle automatic lathes. Still more particularly, the present invention relates to an arrangement for advancing rod stock pieces in such turning machines.
It has been proposed to feed a plurality of rod stock pieces to a work station of an automatic turning machine by advancing a movable slide member. The slide member has a hollow spindle which surrounds a respective rod stock piece, and a slip clutch mechanism which advances the surrounded rod stock piece only when the slide member is moved in direction towards the work station. The slide member is reciprocally moved by pressurizable air cylinders.
However, such prior-art constructions have the disadvantage that the feeding time is dependent upon many variables. For example, the time required to advance successive workpiece portions of the rod stock pieces depends upon the operating air pressure of the air cylinder units, the mass of the rod stock pieces themselves, and the frictional relationships between the moving parts. As additional workpiece portions of a single rod stock piece are cut away, the residual length of the respective rod stock piece becomes correspondingly reduced. This means that the mass and frictional characteristics of the residual rod stock piece are constantly decreasing, a fact which must be considered particularly during acceleration of the rod stock piece towards a work station.
For quick-working automatic turning machines, the clampable jaws which hold a respective rod stock piece must open and close within very short time intervals. The pressurized air cylinders of the prior art have proven to be highly unsatisfactory in advancing the rod stock pieces through such jaws in the required time intervals. In order to accommodate such quick-working machines, the air cylinders must be operative to accelerate the respective rod stock piece to extremely high values. This is further disadvantageous in that very high air pressure magnitudes are required which, in turn, causes the leading end of the respective rod stock piece to impact against an automatic stop of the turning machine with a relatively high impact force. In extreme cases, the leading end of the respective rod stock piece strikes the stop at such high energy that deformation of the leading end occurs.